Muffle



H. H. HARRIS MUFFLE Filed Aug. 17, 1937 INVENTOR rw WM ow 6 H ATTORNEY-5Patented Jan. 31, 1939 UNETEB ears FEE

Application August 17,

13 Claims.

My invention relates to mufiles used in heattreating furnaces, andparticularly to a muffle or like container suspended or otherwisedisposed within a furnace, the articles to be heattreated being placedwithin the muffle or passed therethrough for treatment.

Conventional mufiles are made of cast metal alloy, which renders themboth heavy and eX- pensive, since weight is a cost factor. It is themain object of my invention to make a light and relatively cheap muffle,and I accomplish this by making the muffle partly of cast alloy metaland partly of sheet alloy metal, preferably nickelchromium-iron alloymetal or steel adapted to resist heat and corrosion.

It is also well known in heat-treating practice that sheet metal heatsup and cools down much more quickly than does cast metal, and it is alsoan object of my invention to provide a muffle of cast and sheet metal,the parts of which are so connected that they will heat up and cool downat a fairly uniform rate, especially at and near regions where cast andsheet parts are interconnected.

Further objects of my invention will in part be obvious and in partspecifically pointed out hereinbelow in connection with the followingdescription of an illustrative embodiment In the drawing annexed heretoand made a part hereof,

Figure l is a transverse section through a conventional heat-treatingfurnace, and showing, also in section, one form of mufile constructedaccording to and embodying my invention, suspended therein;

Fig. 2 is a side elevation of the muffle, partly broken away and partlyin section; and

Fig. 3 is a plan View of the muflie, with parts broken away. Furnace Itcomprises side walls l2, l2 and arched roof l4, defining chamber H5within which muffle I8 is suspended by means of chains 22, 22, securedto I-bars 24, 2t, anchored in and through roof M by means of nuts 26,26. Eyebers 24, 24 are preferably angled with respect to each other todistribute the weight load over roof l4 and better support the muffleweight.

By suspending the muffle preferably from above, 50 I am enabled toutilize the weight of the mufile and of its contents for holding thesheet portions thereof in a state of extension or semirigidity and tothereby dispense with need for braces, stiffeners, and the like, for thesheet metal portions. The drawing illustrates one way 1937, Serial No.159,480

of suspending a mufile within the furnace chamber, but this can be donein various ways.

The wall members of mufile I8 comprise cast portions 28, 28 and sheetportions 30, 32, of heat and corrosion resisting alloy metal. Cast 5portions 28, 28 form the upper corners of the muflie and are providedwith upwardly extending ears 3 3, 34 to which the suspending chains 22,

22 are secured. The corner bars 28, 28 are preferably identical, and areprovided with a central l0 depression 29 with the inner and outer edgescurving down and inwardly in a reverse direction from the depressedmiddle. In cross-section the curvature near the edges of bars 28 isalmost semi-circular, and the cars 3 34 are dis posed in the centraldepression 29. Sheet 30 is welded on to the upper convex surfaces of theinner parts 36, 36, of bars 23, 28 to form the top wall of the muffleAll. A preferably continuous sheet 32 is welded to the convex outersurfaces of the other side portions 38, 38 of corner bars 28, 28, andserves in the form shown to form the sides and bottom walls of themufile.

The floor ill of the muffle is disposed within and supported by the sideand bottom wall sheet 32. In forming the floor 40 a plurality ofcrossbeams 42 are disposed transversely within the muffle. Each beam :12has a semi-circular notch 44 at the end thereof to receive a tube 48extending lengthwise of the muffle. Tubes 46 are supported by the sheetwall member 32 and in turn support the cross-bars 52 and floor 40. Thusan extended rounded engagement is provided at $8 between sheet 32 andthe outer rounded surfaces of tubes to thereby avoid any possibility ofproducing a crack or break in the sheet member 32 at the region where itserves to support the floor 40.

The weight of the floor members and the contents of the muflle serves toput sheet 32 under tension, and this tension is taken up and absorbed.by the curved sin-face weld connection 52. Thus the sheet wall parts 32remain substantially rigid without reenforcing or bracing. Sheet 311,comprising the muffle roof or hood is under no particular tension otherthan its own weight, and may permissibly sag centrally, as shown.

The connections between cast and sheet members comprise broad overlapsas shown, and the welded connections are-made at and near the edges ofthe sheet portions with the principal part of the overlap consisting ofthe sheet resting freely upon and in contact with a convex surfaced partof cast metal. The cast metal edges as 49 55 are turned in so as to faceaway from the sheet metal and not to contact the sheet, thus avoidingany injury to sheets from sharp edges of cast metal. The marginal partsof the sheets thus heat up and cool off with the rounded cast metal withwhich they are in contact. Thus the welded joints between the cast metaland sheet metal are relieved from strains caused by uneven heating andcooling rates of thin sheet metal and thicker cast metal as will bereadily understood. When an extra-long muffle is desired, I weldtogether end to end a plurality of sections, as shown at 56. To keep themuflle from swinging within the furnace, and putting extra strain on thesuspending mechanism, as may occur in loading and unloading, I provide apin or pins 58 on the underside thereof to be received within a track orchannel (not shown) on the furnace floor. The floor 40 preferablycontains the work-supporting tracks 40a.

My improved muflle is much lighter and cheaper than mufiies madeentirely of cast alloy, for example. Increased efficiency is secured bymaterially reducing the time required for the heat treatment operation,the sheet wall portions heating up rapidly and transmitting heat rapidlyto the articles being treated.

I claim.

1. A mufile for use under suspension within heat-treating furnacescomprising curved cast metal upper corner bars, and sheet steel top,side and bottom portions, said sheet metal portions being welded to thecast corner bars and also extending along and around the curved portionsof said bars.

2. A muflle as in claim 1 in which the cast steel corner bars curveinwardly of the muffle and the sheet portions overlie said curved castportions.

3. A muflle as in claim 1 in which the edges of the cast bar portionscurve away from the sheets, and the first points of contact betweensheet metal and cast metal are removed substantially in from the edgesof said cast bar portions.

4. A mufile as in claim 1 in which broad, rounded overlaps are providedwhere the cast and sheet metal portions meet, and the Welding is at theextreme edge of the overlapping sheet portion around the curve of thecorner bars.

5. A mufiie for use in heat-treating furnaces comprising a pair ofrigid, self-sustaining cast metal bar portions forming the upper cornersof the muflle, a semi-rigid sheet metal portion welded thereto formingthe roof of the muffle, and a second semi-rigid sheet metal portionwelded to said cast portions and forming the sides and bottom of themuflle.

6. A muflle as in claim 5 in which the cast metal upper corners arecurved, and curve inwardly of the muffle.

'7. A muflle for use under suspension within heat-treating furnacescomprising a pair of rigid,

self-sustaining cast metal bar portions forming the upper corners of themuffle, means secured to said cast upper portions whereby the muflle maybe supported within a furnace, a semi-rigid sheet metal portion weldedto said cast portions and forming the sides and bottom of the muflle,and means to place said second referred to sheet portion under tension.

8. In a heat-treating furnace comprising a floor, walls and roof, amuflle comprising a pair of rigid cast metal bars forming the uppercorners of the mufile, a semi-rigid sheet steel portion welded theretoforming the roof of the muflle, a second semi-rigid sheet steel portionwelded to said cast portions forming the sides and bottom of the muflle,and means to suspend said muflle within the furnace to permit the weightof muffle and contents to place said second semi-rigid sheet steelportion under tension and keep it from buckling.

9. A muiiie as in claim 8 for use under suspension within heat treatingfurnaces in which the cast metal corner bars curve inwardly of themuflle and the sheet portions overlie said curved corners and are weldedthereto at the extreme edges of the overlapping sheet portions.

10. A heat-treating furnace as claimed in claim 8, in which the means tosuspend said muflle comprises ears on said cast corner bars secured tochains and eyebars anchored in the roof of the furnace, the chains andeyebars diverging upwardly from the muflle toward the roof.

11. In a heat-treating furnace comprising a floor, sides and a roof, amuflle comprising a pair of rigid, self-sustaining cast metal barportions defining the upper corners of the muffle, a sheet metal portionwelded thereto forming the roof of the muflle, a second sheet metalportion welded to said cast bar portions and forming the sides andbottom of the muflle, means to place said first referred to sheet metalportion under tension comprising a suspending connection of the mufflewithin the furnace, a floor within and supported by said second referredto sheet steel portion, the weight of the floor and muflle contentsserving to keep said second sheet metal portion under tension.

12. In a heat-treating furnace as claimed in claim 11 wherein thetransverse beams have notched ends, and a tube is disposed within saidnotches, which tube extends lengthwise of the furnace, whereby thesecond referred to sheet will pass around a curved edge.

13. In a muflle comprising a suspended sheet metal wall and bottomportion, a floor structure within said sheet metal portion and saidfloor comprising round sectioned parts at its edges, and said floorbeing supported by said sheet metal portion by engagement thereof withthe rounded edge portions.

HENRY H. HARRIS.

